Method of cracking oil



H. SYDNOR METHOD OF CRACKING OIL Filed March 20, 1931 .clclu v Patented Oct. 1.1935

unwrap STATES PATENTOFFICE METHOD OF CRACKING 01L Harold Sydnor, Elizabeth, N. .I.,'assignor to E Standard Oil Develop ration of Delaware ment Company, a corpo- Application March 2 0, 1931,Serlal N... 524,661,

mm. (01. 196-51) A X This invention relates to improvements in the operation of cracking equipment of a the tube and tank type in which the flow of oil in the tank or digesting drum is from the top to the bottom;

it. and the maintenance of the drum release-linein a clean condition;

. Another object of the invention is to provide [a plurality ofcracking circuits preferably heated bya-common source of heat and both discharg-- ing into the upper portion of the digesting drum.

Stocks of diverse character are to be heated under different conditions in the various circuits.

Referring to the drawing, which is a side elevation, partly in section, showing a preferred form of equipment, reference numeral I indicates a line through which the oil to be cracked. preferably crude petroleum oil, is fed into the heat exchange system. This comprises closed coils 2 and 3 arranged respectively inthe upper parts of fractionating towers 4' and 5, and a tar heat exchanger 6. The oil so preheated is passed intothe intermediate portion of tower 4 where it comes into direct contact with the reflux formed in the upperpart of thetower.

The amount of heat acquired by the oil in passing through the heat exchange equipment is sufhcient to vaporize the gasoline and naphtha contained in it. The conditions in tower '4 are so controlled that the gasoline passes overhead through a line I to cooling coil 8 and suitable storage not shown, while the heavy naphtha is withdrawn through a line 9 into an accumulator I I.

The cracking furnace ll contains two tube circuits l2 and IS. The second of these la erranged in the hottest portion of the furnace adiacent the burners 14. The first circuit I2 is arranged in the cooler part of the furnace. I

Circuit I2 is supplied with gas oil from tower 5. This gas oil is withdrawn from the bottom of tower 5 by line I! through pumps l6 and thence into the inlet of circuit l2. Heavy naphthais supplied to circuit i3 through line H, pump i8, inter-condenser l9 and line 20.

The circuits l2 and I 3 discharge respectively through lines 22 and 2| into a common line 23 opening into the upper part of the digesting drum 24. The release line 25 from this drum enters it at a point rather close to its bottom. A

- trolled according to this invention, in two ways:

pressure control valve 2! is installed in line". A separator 21 receives the oil discharged through line 25. .Vapors are discharged from the sepa rator through a line 28 into indirect heat ex-. change with the oil passing through interecon- I denser Is and thence into the-intermediate portion of tower 5. This tower as well as tower 4 is provided with suitable fractionating means such as bellcap plates 29. Oil may be by-passed if desired from tower 4 to tower I through line 30. In this line there is a control valve 3|.

Cracking conditions in the drum 2 4 are con First by adjusting the relative amounts and heat content of the two streams of oil from the cracking circuits; and. second by the introduction of relatively cool oil in the lower part of the drum. This latter is preferably accomplished by the drawing of the oil from the lower part of tower 4 through line 32 and pump 33, and injecting the 1 oil into the drum at a point adjacent the inlet of the release line therefrom. It will be noted that the oil so supplied to the bottom of the drum is the crude oil reduced by flash vaporizationin the tower 4. According to the present invention,

. this is an entirely practical and advantageous optains' relatively large amounts of heavy components. Such oil would be detrimental in a digesting drum operating on the principle of inlet at the bottom and outlet at the top. The heavy components of the introduced oil would tend to settle and accumulate in the drum where they would be converted into coke.

When operating with inlet at the top and outlet at the bottom the oil introduced does not have a chance to collect in the drum. It remains therein long enough however to have a solvent eifect on the heavy material which tends to form by polymerization of the oil in the drum. The introduced oil tends to flux these, polymers and permits them to be readily carried oil. In this way the amount, of coke formed is greatly reduced. While some of the advantages of the invention may be obtained by introducing the relatively heavy oil into the lower part of the drum at any point, best results are obtained by injecting it as shown. The oil is in part forced into the outlet line and keeps the line clear of coke.

The method described above can be operated under a rather wide variety of conditions. The following is given by way of example.

Crude oil is passed into the system through line I and is stripped of its lighter fractions in tower 4 as described. The stripped oil from It tower 4 i'spassed through line 32 into drum 24 at apoint adjacent release line 25. The temperature in circuit i2 is 900 to 925 F. and it is testy gas oil from tower 5. i'he temperature in circuit I3 is 950 to 975 F. and it is fed from the heavy naphtha accumulator i0, which reelved its oil from the upper part of tower 4. It wm be-noted that this naphtha is straight-run. There are substantial advantages in. cracking such naphtha at high temperature substantially invapor phase as distinguished from recracking cracked naphtha. y

The circuits and the digestinggdrum are held at a pressure of 700 to 800 lbs. per square inch.

"me temperature in the separator vim be about The amount oi'oil to be introduced in'the bottom of drum 24 will be determined by various conditions. In general it may be said. that all thereduced crude remaining after an removal oi. the gasoline and naphtha may be passed into the drum as described. However, ii desireda part of this reduced crude may be withdrawn from tower 4 through line 34. The reduced crude is thus subjected to high temperature conditions and the recovery of lower boiling components outlet pipe II. In the cracking circuits the gas oil, will I usually be mostly in liquid phase and the heavy naphtha at least partly in vapor phase.

novelty inherent in the invention as broadly as the prior art permits. p I claim: g

Process of cracking 011 comprising reducing a crude oil by flash vaporization to obtain a reduced crude oil, collecting a heavy naphtha and a light naphtha distillate substantially free from cracked products from such crude oil, heating the heavy naphtha to a cracking temperature under pressure in an elongated narrow heating zone and introducing it into the upper part of an enlarged vertical digestion zone, heating gas oil to a cracking temperature lower than the above mentioned cracking temperature under pressure in a separate elongated narrow heating zone and introducing it into the upper part (if said enlarged vertical digestion zone, the reduced crude oil from which naphtha has been removed into the lower part 01' such zone in the hot state as "obtained from the reducing operation, removing oil and vapor together from the 

